Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C Product information presented is for internal use within AAT Inc. only. Details are subject to change without notice 2A 15V Step-Down DC-DC Converter FEATURES GENERAL GENERAL DESCRIPTION Buck PWM with Internal PMOS The AAT1346A/B/C is a 2A 15V step-down converter, 4.5V to 15.0V Input Voltage Range which provides an integrated one-channel PWM Max. 2A Output Current Under-Voltage Lockout (UVLO) Protection power supply circuitry for specific applications. Internal Short Circuit and Thermal Protection The buck PWM contains enable control signal, error Internal Soft-Start amplifier, Fixed Switching Frequency (380kHz / 47kHz) under-voltage 2 µA Shutdown Current SOP- 8 Package solution for the power supply of DC-DC system. It offers system engineers the flexibility to tailor-make the PWM comparator, protection, output oscillator, short driver, circuit protection and voltage reference circuit. The AAT1346A/B/C contains one buck current mode PWM with internal PMOS. In addition, a digital soft-start is also included to prevent inrush current at startup. AAT1346A/B/C comes with a fixed 380kHz PIN CONFIGURATION oscillator, however, when the feedback voltage is lower than 0.7V, the switching frequency changes to 47kHz and returns to 380kHz after the short-circuit is released. TYPICAL APPLICATION Power In VDD EO ENC – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 1 of 12 VOUT SW IN ENC GND Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C ORDERING INFORMATION DEVICE TYPE PART NUMBER PACKAGE PACKING TEMP. RANGE MARKING MARKING DESCRIPTION AAT1346A AAT1346A-S-T S:SOP8 T: Tape and reel 40 C to +85 C AAT1346A XXXXXX Device Type Lot no.(6~9Digits) AAT1346B AAT1346B-S-T S:SOP8 T: Tape and reel 40 C to +85 C AAT1346B XXXXXX Device Type Lot no.(6~9Digits) AAT1346C AAT1346C-S-T S:SOP8 T: Tape and reel 40 C to +85 C AAT1346C XXXXXX Device Type Lot no.(6~9Digits) NOTE: All AAT products are lead free and halogen free. ABSOLUTE MAXIMUM RATINGS PARAMETER SYMBOL VALUE UNIT Supply Voltage ( VDD , SW) VDD −0.3 to 15.0 V Pin Voltage (IN, ENC, EO) VI −0.3 to ( VDD +0.3) V SW Current ISW 6.5 A Operating Temperature Range TC −40 C to +85 C C Tstorage −65 C to +150 C C Storage Temperature Range – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 2 of 12 Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C ELECTRICAL CHARACTERISTICS ( TC =25 C , VDD = 12V, Unless Otherwise Specified) GENERAL ITEM PARAMETER SYMBOL VDD Input Voltage Range Under Voltage Lockout VUVLO Under Voltage Lockout Hysteresis VUHYS Input Current into VDD TYP 4.50 VDD Falling 3.33 3.48 MAX UNIT 15.0 V 3.63 V 150 mV VIN = 1.5V 1 mA IDD_ON VIN = 1.0V 5.5 mA ISHDN OSC Frequency fOSC VSHORT EN Low Level VIL EN High Level VIH Thermal Shutdown MIN IDD_OFF Shutdown Current into VDD Short Detection Voltage TEST CONDITION 1.70 10.0 µA Normal Operation 380 kHz Short-Circuit 47.5 kHz VIN Falling 0.67 0.70 0.73 V 0.4 V 1.6 TSHDN V 160 C BUCK PWM PARAMETER SYMBOL TEST CONDITION MIN TYP MAX UNIT IN Regulation Voltage VIN IN=EO 1.209 1.222 1.235 V IN to EO Transconductance Gm IN=EO 35 80 125 µS Maximum Duty Cycle 90 IN Input Leakage Current IL Current-Sense Amplifier Transresistance RCS SW Leakage Current ILSW Switch On-Resistance RON SW Current Limit ILIMIT IN=0V to 1.5V VSW = 15V 0.1 2.5 – 台灣類比科技股份有限公司 – – 0.01 +100 Advanced Analog Technology, Inc. – Version 1.00 Page 3 of 12 nA V/A 0.2 t SS Soft-Start Time −100 % 5.0 µA 200 mΩ 3.7 A 700 µs Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C PIN DESCRIPTION PIN NO. NAME I/O 1, 2 NC - Not Connected 1 3 VDD I Power Input 3 7, 8 4 SW I/O 4 5, 6 5 GND - Ground 5 4 6 IN I Feedback Input 6 3 7 EO I/O 7 2 8 ENC I Enable Control 8 - - NC - Not Connected A B C 1 - 2 FUNCITION Switching Node Error Amplifier Compensation Output FUNCTION BLOCK DIAGRAM DIAGRAM AAT1346A/B/C – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 4 of 12 Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C TYPICAL OPERATING CHARACTERISTICS ( VIN =12V, TC =25 C Unless Otherwise Noted) AAT1346A – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 5 of 12 Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C TYPICAL OPERATING CHARACTERISTICS CHARACTERISTICS (CONT (CONT.) ONT.) ( VIN =12V, TC =25 C Unless Otherwise Noted) – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 6 of 12 Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C TYPICAL OPERATING CHARACTERISTICS (CONT (CONT.) ONT.) ( VIN =12V, TC =25 C Unless Otherwise Noted) – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 7 of 12 Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C TYPICAL APPLICATION CIRCUIT AAT1346A/B/C – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 8 of 12 Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C DETAILED DESCRIPTION DESIGN PROCEDURE The AAT1346 is a current-mode buck switch-mode Programming the Output Voltage regulator with a fixed switching frequency of 380kHz. It The output voltage for the AAT1346 is programmed uses an internal P-channel MOSFET switch to step using a resistor divider from the output connected to down the input voltage to the regulated output voltage. the feedback pins (Figure 1). When setting the output The converter regulates input voltages from 4.75V to voltage, connect a resistive voltage divider from the 15V down to an output voltage as low as 1.222V, and is output to IN pin and then to GND. Choose the able to supply up to 2A of load current. lower-side (IN-to-GND) resistor, then calculate the ENC Control Input upper-side (output-to-IN) resistor as follows: V R upper = Rlower out − 1 V IN The AAT1346 contains built-in pull high logic. The IC is enabled when ENC becomes floating (ENC pin voltage ＞ 1.6V). When the voltage is lower than 0.4V, the IC is disabled. Where VIN is the feedback regulation voltage, 1.222V (typ). Typical values for Rlower are in the range of 10kΩ to 100kΩ. Soft-Start The AAT1346 has built-in 700 µs soft-start time. Upon power turn-on, if ENC pin is not pulled low; and VDD is above VUVLO (typ. 3.48V), IN pin will climb from 0V to 1.222V during 700 µs soft-start time to reduce inrush current. Short Ciecuit Protection When short circuit happens, and the feedback voltage Figure 1. Feedback Network (IN) is less than 0.7V, the switching frequency will change to 47kHz to reduce the power supply from input to output to protect the system. The frequency will switch back to 380kHz after the short circuit is released. Inductor Selection A good rule of thumb when choosing the inductance is to allow the peak inductor current in the inductor to be approximately 115% of the maximum load current. Also, make sure that the peak inductor current is below the Thermal Shutdown The AAT1346 includes a thermal-limit circuit that shuts down the IC at approximately +160°C. The part turns on after the IC cools by approximately 20°C. 2.5A minimum current limit. The inductance value can be calculated by the equation: V Vout ⋅ (1 − out ) Vi L≈ 0.3 ⋅ Iout ⋅ fSW Where Vout is the output voltage, Vi is the input voltage, fSW is the switching frequency (380kHz), and – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 9 of 12 Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C Iout is the maximum load current. When the inductance value is determined, then the peak inductor current can be calculated by the equation: V Vout ⋅ (1 − out ) Vi IL(peak ) = Iout + 2 ⋅ fSW ⋅ L setting approximately as follows: Vout ⋅ (1 − Vripple ≈ Vout ) Vi 8 ⋅ L setting ⋅ C out ⋅ fSW 2 Where Vout is the output voltage, Vi is the input voltage, fSW is the switching frequency (380kHz), Where Iout is the maximum load current, Vout is the Cout is the output capacitance, and L setting is the output voltage, Vi is the input voltage, fSW is the inductance value. switching frequency (380kHz), and L setting is the If the capacitor has significant ESR, the output ripple inductance value. Choose an inductor that does not component due to capacitor ESR is as follows: saturate under the peak inductor current. Vripple ≈ 2 ⋅ (IL(peak ) − Iout ) × RESR Schottky Diode Selection Choose a Schottky diode whose maximum reverse voltage rating is greater than the maximum input voltage, and whose current rating is greater than the peak inductor current. The AAT1346 employs current-mode control, thereby The input capacitor in a DC-to-DC converter reduces current peaks drawn from the input power source and switching ESR. Compensation Input Capacitor reduces Where IL(peak) is the peak inductor current, Iout is the maximum load current, and RESR is the capacitor’s noise in the controller. The impedance of the input capacitor at the switching simplifying the control-loop compensation. When the AAT1346 operates with continuous inductor current (typically the case), a RLOAD COUT pole appears in the loop-gain frequency response. To ensure stability, frequency should be less than that of the input source set the compensation RC CC to zero to compensate so high-frequency switching currents do not pass for the RLOAD COUT pole. Set the loop crossover through the input source. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also satisfy. For insuring stable operation the IC must be bypassed with a 0.22 µF ceramic capacitor placed close to the VDD . below the lower of 1/10 the switching frequency (380kHz). The compensation resistor and capacitor are then chosen to optimize control-loop stability. Choose the compensation resistor RC to set the desired crossover frequency fC . Determine the value by the following equation: Output Capacitor The output capacitor keeps output ripple small and RC = ensures control-loop stability. The output capacitor must also have low impedance at the switching 2π × COUT × VOUT × R CS × fc Gm × VIN Where Cout is the output capacitance, Vout is the frequency. Ceramic, polymer, and tantalum or low-ESR output voltage, RCS is the current-sense amplifier electrolytic capacitors are suitable. transresistance (0.2V/A), Gm is the error amplifier Output ripple with a ceramic output capacitor is transconductance (80 µS ) and VIN is the feedback – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 10 of 12 Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C threshold voltage (1.222V). If the value calculated for RC is greater than 100 kΩ , 100 kΩ is recommend. Choose the compensation capacitor CC to set the zero to 1/4 of the crossover frequency. CC < LAYOUT CONSIDERATIONS CONSIDERATIONS Conductors carrying discontinuous currents and any high-current path should be made as short and wide as possible. The compensation network should be very close to the EO pin and avoid through VIA. The IC must be bypassed with a 0.22 µF ceramic capacitor COUT × VOUT 4 × RC placed close to the VDD. Tie the feedback resistor divider to be very close to output capacitor and far If the output filter capacitor Cout has significant ESR, away from the inductor or Schottky diode. Keep the a zero occurs at the following: feedback network IN close to the IC. Switching nodes (SW) should be kept as small as possible and should ZESR = be routed away from high-impedance nodes such as 1 IN. 2π × C OUT × RESR If ZESR > fC /4, it can be ignored, as is typically the case with ceramic output capacitors. If ZESR < fC /4, it should be cancelled with a pole set by capacitor Cp connected from EO to GND: CP = C OUT × RESR RC If Cp is calculated to be <10pF, it can be omitted. – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 11 of 12 Advanced Analog Technology, Inc. June 2008 AAT1346A/B/C PACKAGE DIMENSION SOP- 8 Symbol A A1 A2 b C D E E1 e L y θ Dimensions In Millimeters MIN TYP MIN 1.35 1.60 1.73 0.05 -----0.15 -----1.45 -----0.33 0.41 0.51 0.19 0.20 0.25 4.80 4.85 4.95 5.79 5.99 6.20 3.81 3.91 3.99 1.27 BSC 0.406 0.710 1.270 ----------0.076 0˚ -----8˚ – 台灣類比科技股份有限公司 – – Advanced Analog Technology, Inc. – Version 1.00 Page 12 of 12